A typical cellular wireless communication system provides numerous wireless coverage areas in which served wireless communication devices (WCDs) can operate. Each wireless coverage area is defined by radio frequency radiation from a respective cellular base station, and each base station, together with additional network infrastructure, may provide connectivity with one or more transport networks such as the public switched telephone network (PSTN) and the Internet. With this arrangement, a WCD that is positioned within a given wireless coverage area may be served by the base station defining that coverage area and may thereby engage in communication, via that base station and perhaps additional network infrastructure, with one or more other WCDs, network servers, and other entities.
In practice, a base station may radiate to define one or more wireless coverage areas and may periodically broadcast in each coverage area a set of system information for receipt and use by WCDs operating in the coverage. Such system information may take various forms. By way of example, the system information may include information that enables WCDs to operate in the coverage area, such as information about channel configuration and access parameters for instance. Further, the system information may include information that enables WCDs to evaluate and possibly hand off to other coverage areas, such as identifiers and operational parameters of neighboring coverage areas for instance.
From time to time, the system information that is periodically broadcast in a given coverage area or group of coverage areas may change, due to engineering input or dynamically according to a schedule or in response to evaluation of network conditions for instance. When that happens, it may be important for the WCDs operating in the coverage area to read the updated system information and update their settings accordingly. As WCDs are typically battery powered, however, it is impractical to have WCDs read the system information every time the base station broadcasts it. Consequently, many systems are instead (additionally) arranged to have each base station periodically broadcast a small “tag value” that may serve to indicate when the system information is changed, so as to trigger re-reading of the system information when appropriate.
In practice, for instance, the tag value may be a Boolean value, and the base station may be arranged to toggle the value between zero and one each time the system information changes. Alternatively, the tag value may be a binary word or byte (or the like), and the base station may be arranged to cycle through values of that binary word or byte, incrementing by one each time the system information changes. Once a WCD has read and stored the full set of system information broadcast in a coverage area, the WCD may then be arranged to periodically read just that tag value instead of the full set of system information. If and only if the WCD thereby determines that the tag value has changed, the WCD may then read the updated full set of system information. Thus, if the WCD does not detect that the tag value has changed, the WCD may forgo reading the full set of system information, thereby helping to conserve its battery power.